Strong Upper Limits on Sterile Neutrino Warm Dark Matter · 2008. 10. 24. · Sterile neutrino WDM...
Transcript of Strong Upper Limits on Sterile Neutrino Warm Dark Matter · 2008. 10. 24. · Sterile neutrino WDM...
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Hasan Yüksel, John F. Beacom & Casey R.
Watson, Phys. Rev. Lett. 101, 121301 (2008)
Masaki Mori
Strong Upper Limits on Sterile
Neutrino Warm Dark Matter
ICRR CANGAROO group internal seminar, October 24, 2008
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A news in physicsworld.com
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Dark matterの分類 Hot dark matter
宇宙初期に熱平衡 クォーク・ハドロン相転移以降に粒子数がFreeze
< 1 MeVニュートリノ Free streaming dampingにより短いスケールの揺らぎは消えるため、宇宙の構造形成はトップダウン型(銀河がつくれない!)
Warm dark matter 宇宙初期に熱平衡 クォーク・ハドロン相転移以前に粒子数がFreeze
0.1-100 keV Sterile(「非活性」)ニュートリノ
Cold dark matter 粒子が非相対論的な時期に粒子数がFreeze、あるいは熱平衡に達することがない
> 1MeVニュートリノ、アクシオン、WIMP (Weakly Interacting Massive Particle: ex. ニュートラリーノ)
揺らぎはスケールによらないため、ボトムアップ型の構造形成が可能
H. Nunokawa, lecture note (1993)
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初期宇宙における相互作用の分化
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初期宇宙での温度降下によって真空の相転移が起こり相互作用が分化してきたという,現代の「力の統一理論」のパラダイムを表現した図 (佐藤文隆、1976)
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Sterile neutrino
LEP→ニュートリノの世代数は2.987±0.016
弱い相互作用する標準理論のニュートリノのみ
Sterile neutrino: 重力のみで相互作用
右巻きニュートリノor 左巻き反ニュートリノ
Dirac質量で通常のニュートリノと混合
Majorana質量も可能
Seasaw機構で通常のニュートリノは軽く、Sterileニュートリノは重くなりうる
νMSMモデルではGeV-keVの質量
Particle Data Book 2008
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LRRLmL
h.c. L
c
LmL
R
L
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Dark matterと構造形成
ΛCDM (Λ[cosmological constant]+Cold dark matter)の問題点
観測されるより多くの小規模構造
3D計算に見られる銀河中心での密度過剰
Warm DM
< 0.25Mpc(mX/keV)-4/3の構造形成はsuppress観測に合致
宇宙の再電離を遅らせるWMAP3の結果で制限
Sterile neutrino WDMについての間接的制限 CDMの小規模clustering
3D galaxy power spectrum
Lyman- forest
ms >1.7keV or ms >14 keV (simulation依存などで議論あり)
バリオン数やレプトン数の非対称性や、元素合成などにも影響
Watson et al. PR D74, 033009 (2008)
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Plausible mass and mixing parameters
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Gouvea, Jenkins & Vasudevan, PR D 75, 013003 (2007)
for WDM
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Sterile neutrino WDM model
Predominantly decay to 3 (=e,,)
Radiative decay s e,, + (Dirac mass)
X-ray luminosity
X-ray line fux at E,s = ms/2
Density-production relationship (assuming TQCD=170MeV and nb/n=10-10)
∴
Watson et al. PR D74, 033009 (2008)
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=1/
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Sterile neutrinoの放射崩壊による制限 ラインX線:E,s = ms/2 via s e,, +
Cosmic X-ray Background (CXB) XMM/HEAO-I: ms <9.3 keV [Boyarsky et al.
2006]
Galaxies/clusters Vir A (M87): ms <8.2 keV [Abazajian 2006]
Vir A, Coma: ms <6.3 keV [Abazajian & Koushiappas 2006]
Andromeda: ms <3.5 keV [Watson et al. 2006]
Watson et al. PR D74, 033009 (2008)
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INTEGRALラインガンマ線探索
Teegarden and Watanabe (2006)
Point and diffuse sources in the Milky Way
SPI data, 20-8000 keV
Tested for lines of intrinsic width 0, 10 100 & 1000 keV
Large-scale regions around Galactic center
13 degreer (exposure 1.9106s) and 30 degreer (3.6106s)
Upper limits on flux from an unknown line emission
Average flux away from GC (>30deg) was subtracted – cancels
all cosmic signal and part of halo signal
Limits around GC: <10-4photons cm-2s-1 (3.5)
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Milky Way dark matter decay flux
Photon flux within an angle from GC
Dimensionless line of sight integral (Rsc: solar circle)
∴
Number of photons within
Lower bound for the integral when sc is constant within
Rsc: J()~2, =2(1-cos )=0.16 (for =13)
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Milky Way dark matter decay flux (cont.)
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Realistic dark matter density profile:
NFW / Moore / Kravtsov profiles
Durret et al., AA 432, 809 (2005)
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Upper limits from subtraction
0.5 (conservative limits for =13)
3 times larger limit for =30, but flux is also 2-3 times larger
Results are rather robust against angular region
Constraints on mass and mixing: flux < INTEGRAL limit
(next page figure)
This assumes sterile neutrinos comprise all of the required
dark matter.
Constraints on sterile neutrinos
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Mass and mixing parameter space
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Now plausible
in only this
region!
“Hope fades for neutrino dark matter…”
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Previous limits
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Smirnov & Zukanovich Funchal, PR D74, 013001 (2006)